In high speed bottle labeling, paper manufacturing, and other similar industries where a web of thin material such as polymer film or paper is withdrawn from a rotatably mounted supply roll, a braking force is typically applied onto the assembly supporting the supply roll to ensure that uniform tension is maintained on the withdrawn web material as it is processed. These supply rolls have high inertia which varies as the roll unwinds and its diameter decreases.
The amount of braking force applied onto the support assembly is usually varied depending on the diameter of the roll and its inertia to maintain constant web tension. During acceleration and deceleration of the supply roll, the braking force on the support assembly must change to maintain the desired web tension and prevent either film breakage caused by excess back tension or prevent overrunning of the web feed caused by a lack of proper tension. Deceleration to a rapid stop position is also difficult because the supply roll can overrun when no additional braking force is applied to compensate for such rapid deceleration. As a result, during rapid supply roll slowdowns into a stop position, additional braking force must be applied on to the support assembly to prevent overruns.
Various prior art systems have been devised to accomplish controlled deceleration into a stop position while preventing overruns. In some processing lines, the operator manually adjusts the tension on the applied web material. Manually adjusting the web tension, however, can be inaccurate depending on the reaction time and accuracy of the operator. Other systems automatically apply an additional braking force during deceleration, but often these systems are complex, using line speed measurement devices which combine their output signals with output signals corresponding to measured inertia changes. Corresponding changes in applied tension then are made based on changes in the line speed and the diameter of the supply roll. Also, in some prior art systems, no compensation is made for the rotational inertia of the support assembly holding the supply roll. Depending on the size of the web roll, the rotational inertia of the support assembly can have a major impact on the amount of braking force that should be applied during stopping operations.
In many web processing lines, the production requirements vary depending on the desired end product. A first production run at the start of a shift may require wide, heavy, large diameter rolls of web material. In this instance, the inertia is primarily in the supply roll itself, and not in the assembly supporting the roll. A stop signal would not have to compensate extensively for the inertia of the support assembly. Other production runs later in the shift, however, may require narrow width, small diameter, lightweight supply rolls, where the inertia of the support assembly has a greater impact on the stopping operation. Thus, the stop signal would have to compensate for the inertia and greater impact of the support assembly.
Therefore, it would be desirable if a more efficient and less complex system were used that generated a stopping signal to a braking mechanism of a supply roll support assembly which not only compensated for the varying supply roll diameter, but also compensated for the rotational inertia of the support assembly.